1. Field of the Invention
The invention relates to an apparatus and method for producing electronic elements, and more particularly to an apparatus for fixing a conductive wire such as a bonding wire to a bonding pad of electronic elements and to a method thereof. In addition, the invention relates to an electronic elements producing apparatus which is used to connect bonding pads of an electronic element such as a semiconductor device and leads of a package in which the electronic element is packaged with a thin metal wire, and to a method thereof.
2. Description of the Related Art
Generally, to protect electronic elements such as a semiconductor device from external environments, the semiconductor device is packaged. To supply electric power to the semiconductor device or to input or output a signal to or from the semiconductor device, it is necessary to electrically connect a bonding pad which is formed on the semiconductor device and external terminals such as lead terminals of the package. A wire bonding method is one of methods for effecting such connections. This method mounts a semiconductor device on, e.g., a lead frame which has a plurality of leads and connects the bonding pad on the semiconductor device and the leads with a bonding wire of, e.g., Al or Au.
FIG. 4A and FIG. 4B are diagrams showing an example of the connecting step of the bonding wire and the bonding pad in a conventional wire bonding method. These drawings are partly enlarged sectional views showing the leading end of a bonding tool and the bonding pad of a semiconductor device. It is shown that a bonding pad 96 is formed on a semiconductor device 95, and a bonding wire 93 is being bonded to the bonding pad 96.
As shown in FIG. 4A, the bonding wire 93 is passed through a through hole 92 of a bonding tool 91 which is generally called a capillary, and the leading end of the bonding wire 93 protruded from the through hole 92 has a ball 93b formed by, e.g., an electrical spark. This ball 93b prevents the bonding wire 93 from being pulled into the through hole 92 when the capillary 91 is being moved. And, by forming the ball 93b, a contact area between the bonding wire 93 and the bonding pad 96 can be enlarged to enhance a bonding strength when the ball 93b is pressed against the bonding pad 96.
The capillary 91 is lowered to contact the ball 93b onto the bonding pad 96 as shown in FIG. 4B. And, heat or ultrasonic oscillation is applied to the bonding pad 96 via the capillary 91, and the ball 93b is pressed against the bonding pad 96 by the capillary 91 at the same time. New surfaces are formed on the squashed ball 93c and the bonding pad 96 by th e applied heat or ultrasonic oscillation, and since these new surfaces are mutually contacted, the bonding wire 93 and the bonding pad 96 can be bonded.
But, this conventional bonding method has a disadvantage that the semiconductor device tends to be damaged easily on its portions close to the bonding pad 96 because the bonding pad 96 is directly exposed to an external force such as heat, ultrasonic oscillation or pressure. For example, the disadvantage includes that the bonding pad 96 is separated from an insulator film 97 below the bonding pad 96 and cracks are formed on a semiconductor substrate 98 beneath the bonding pad 96.
And, even when these defects of separation or cracks do not occur during bonding, the semiconductor device 95 which is being used might fail due to an external force which has been applied in the bonding method. Thus, it is difficult to secure satisfactory reliability for the semiconductor device 95.
As described above, the conventional apparatus and method for producing electronic elements had disadvantages that the semiconductor device 95 tends to be damaged easily on its portions close to the bonding pad due to the external force such as heat and ultrasonic oscillation or pressure and that a failure occurs during bonding or even after completing the product.
An object of the invention is to provide an electronic elements producing apparatus and method which can reduce an external force to be applied to the electronic elements and connect a bonding pad and a bonding wire without damaging the electronic elements such as a semiconductor device.
And, another object of the invention is to provide an apparatus and method for producing electronic elements with high productivity which can connect a bonding pad and a bonding wire with a connecting material in a shorter time.